The above-noted parent applications disclose, inter alia, the making of crystalline layered mixed metal hydroxides (MMOH) and various uses of the MMOH compounds as thickening agents and in their use in the making of clay adducts of the MMOH compounds, with preference shown for the monolayer crystal variety made in a flash coprecipitation process. Whereas the flash coprecipitation process produces monolayer crystals, the sequential method of first forming aqueous aluminum hydroxide to which the other metal(s) is/are intimately added as soluble compound(s) (esp. salts) and then precipitated with OH- ions, produces multi-layer crystals, usually 2-layer or 3-layer, or a mixture of both 2-layer and 3-layer. In some instances the layered MMOH compounds can form stacks of the crystals.
There are some applications in which the above-identified multi-layered crystals of MMOH provide certain advantages of their own, including the formation of adducts with clays. These other advantages include, e.g., the ability of the multi-layered MMOH to be concentrated to a higher degree without reducing their ability to react with clays whereas the monolayer variety of MMOH is very concentration sensitive. Also, the multi-layered MMOH does not require a re-dispersing agent as has been found to be needed with the monolayer variety of MMOH, after it has been at dried at moderate temperatures.
As used herein, the term "activated" (a term often used in the field of minerals and inorganic chemistry) refers to the heating (thermal activation) of metal hydroxides or hydrous metal oxides, sometimes in the presence of CO.sub.2, to a temperature high enough to drive off the waters of hydration, leaving the metals as "active" metal oxides or oxy-hydroxides. While one may encounter a chemical method for creating activated metal oxides or oxy-hydroxides, the thermal method would be expected to be the easiest and least expensive method.
The present invention is directed to the making of clay adducts with activated MMOH of the monolayer and the multi-layer variety as well as natural and synthetic hydrotalcites (expressed here simply as MgO.Al.sub.2 O.sub.3 or MgAl.sub.2 O.sub.4 since those are the principal components) and other forms of activated mixed metal oxides or mixed metal oxy-hydroxides (all of which are referred to herein as AHMMO). The activated MMOH (hereinafter sometimes referred to as an AHMMO) and other AHMMO compounds, which are arid, are very friable (easily decrepitated), and easily disperse in water as very small crystals, generally of colloidal size.
For example, hydrotalcite is a naturally-occurring mineral (that contains some CO.sub.2 in its structure) which, when thermally dehydrated, yields an active magnesium aluminum oxide compound or oxyhydroxide compound. Also for example, magnesium hydroxide and aluminum hydroxide can be combined (especially in the presence of some CO.sub.2) and heated to yield mixed metal oxides conforming essentially to the formula (MgO)x Al.sub.2 O.sub.3, where the ratio of Mg/Al can vary over the range of about 0.01/1 to about 6/1, preferably about 0.5/1 to 4/1. Below that range the amount of MgO may not be sufficient to yield a mixed metal oxide which behaves efficiently in the present invention. Above about 4/1, the amount of excess MgO is likely to form a single metal oxide which is present with the mixed metal oxide structure, but as a separate phase.
If heating to ultra high temperatures is done, one may surpass the dehydration temperature at which the activated oxides are produced and can ceramicize or otherwise fuze the oxides into a substantially inert substance. Selection of an appropriate dehydration temperature is within the skill of practitioners of the relevant arts, having learned of this disclosure. Generally, a dehydration temperature in the range of about 400.degree. C. to about 700.degree. C., often about 500.degree. C. to 600.degree. C., is generally sufficient to convert the metal compounds to their activated (dehydrated) oxide or oxy-hydroxide form. Activating other metal compounds (e.g. salts) to obtain the activated oxide form may require more time and/or higher temperature and a more ample supply of oxygen and/or OH.sup.- ions.
U.S. Pat. No. 4,748,139 discloses the thermal activation of mixed metal hydroxides at about 500.degree. C.. These activated mixed metal oxides were then made into dense spinel structures at above 1000.degree. C. Examples are shown starting with Mg(OH).sub.2 mixed with NaAlO.sub.2 and digested at 105.degree. C. to form a layered magnesium hydroxide/aluminum hydroxide which forms MgAl.sub.2 O.sub.4 when heated above 500.degree. C.. Also shown is the making of activated layered CoAl(OH).sub.5 plus Al(OH).sub.3 by starting with cobalt hydroxide and aluminum hydroxide. Further shown is the making of activity CoAl(OH).sub.5 by starting with CaO NaAlO.sub.2. While this patent teaches the making of some activated mixed metal oxides with are useful in the presently disclosed invention, the patent does not teach the formation of an adduct of clay with the activated mixed metal oxides. It only teaches that the precursor compounds (i.e. prior to heating to activation temperature) can be used in combination with clays for use as drilling fluids the like.
Natural clays and refined natural clays may vary from one mining location to another and the performance obtained with one batch may not exactly match the performance of another batch: the color may not match and the effect on viscosity may not match. The natural clays, and even refined natural clays, may contain impurities which can produce non-uniformity among batches and may create side-reactions with other ingredients in a formulation to which the clay is added. Clays are normally anionic and can react with ingredients which are cationic, such as cationic surfactants used in hair conditioners or in cleansers and the like.
U.S. Pat. No.4,318,732 (Sawyer) discloses that the use of unslaked lime (CaO) or calcium magnesium oxide (CaO.MgO), added as a powder to a ground colloidal clay, produces a resultant liquid product of high yield with acceptable stability, based on the contention that the dry mixture of unslaked lime and ground clay can be stored in paper bags for one year without substantial change by reacting with CO.sub.2 from the ambient air. Sawyer discloses that colloidal clays treated with slaked lime (Ca(OH).sub.2) are inherently unstable because of air carbonation (reaction with CO.sub.2). Sawyer also teaches that Wyoming bentonite clay is widely used as a gelling clay but it exhibits the disadvantages of not swelling and not developing viscosity in the presence of flocculating cations or in low to medium ionic concentrations. Wyoming bentonite is known to be a sodium bentonite of the smectite family of clays. Sawyer further teaches that attapulgite and sepiolite are unique performers among the clay mineral thickeners in that they can be used to thicken water solutions of salts that contain high concentrations of ionic materials. The examples shown by Sawyer illustrated attapulgite clay.
Both Ca(OH).sub.2 and Mg(OH).sub.2, which are products formed when their respective oxides are wetted with H.sub.2 O, have a lower limit on pH to remain as dispersions in water. For Ca(OH).sub.2 that lower limit is approximately pH 11.3, and for Mg(OH).sub.2 it is about pH 10. Below these pH values, these hydroxides dissolve and the alkaline earth metal cations, Ca.sup.+2 and Mg.sup.+2 are all that can interact with the clay. Drilling fluids are often run in regimes below pH 10 where it would not be possible to have the Sawyer clay/metal hydroxide adduct because the adduct does not form when the metals are in solution and are present only as their cations, which can react with, but are not "adducts" with, the clay.
Mixed metal hydroxides, on the other hand, are stable over a pH range of about 5 to about 14, and the mixed metal hydroxide clay complexes are also stable over a range of about pH 5 to about pH 14. These complexes do not resemble Sawyer's products: the main thing that Sawyer accomplished was the addition of Ca.sup.+2 and Mg.sup.+2 ions to the clays in a dry state without adding Cl.sup.- ions.